Rugby is played with no helmet no pads. But why are there less injuries than in American football?

I think it’s because the pads and helmets makes the illusion that it’s safer to hit people harder. Also, in football, different positions are more prone to injuries than others and the game isn’t as open field and spread out as rugby is. For example linemen are on average atleast 6’4 350 pounds and constantly are hitting eachother in a stalemate the entire game. Similary, most running backs are significantly smaller but have to run through those linemen.